Stability of 2-thiophenobarbital and its N-methyl derivatives in the presence of beta-cyclodextrin.

The rates of hydrolysis of thiophenobarbital and its N-mono- and N,N'-dimethyl-derivatives were determined under different conditions of pH and temperature using UV spectroscopy. They were compared with those obtained in the presence of different concentrations of beta-cyclodextrin. It was found that the compounds degrade with different rates and beta-cyclodextrin retards the hydrolysis. The formation of complexes between the investigated compounds and beta-cyclodextrin was proved by 13C NMR and ROESY spectra and molecular modeling. The inclusion with the phenyl substituent into the beta-cyclodextrin cavity is preferred.